1. Field of the Invention
The present invention relates to a contour measuring apparatus, and to an apparatus for measuring a contour shape of an object to he measured.
2. Description of the Related Art
Conventionally, a surface property measuring apparatus is used in order to measure properties of a surface, a contour shape, surface roughness, etc. of an object to be measured. The surface property measuring apparatus is an apparatus for tracing a surface of the object to be measured with a stylus of the distal end of an arm and detecting unevenness of each position of the surface by displacement of the stylus in that case and capturing the unevenness as data. As such a surface property measuring apparatus, a contour measuring apparatus for measuring the contour shape of the object to be measured is used.
The known contour measuring apparatus is an apparatus including an arm having a stylus in the distal end, a support mechanism for swingably supporting the arm by bearings, an attitude change mechanism for changing an attitude of the arm and holding the arm in any position within the swing range, a measuring force giving mechanism for urging the arm so that the stylus makes contact with an object to be measured by a predetermined measuring force, and a detector for detecting a swing of the arm as a detecting part (see JP-A-2004-77437).
In JP-A-2004-77437, a cam mechanism abutting on the vicinity of the end opposite to the stylus of the arm is used as the attitude change mechanism. Also, in the measuring force giving mechanism, for example, a coil spring, whose one end is fixed to the vicinity of the support mechanism, arranged an parallel with a shaft of the arm as used as urging means for urging the arm in a swing direction.
In such a contour measuring apparatus, in a state (measurement position) in which the stylus makes contract with a surface of the object to be measured in the side proximal to the object to be measured, the arm is swingably arranged and the stylus is relatively moved along the surface of the object to be measured to thereby measure a contour shape of the object to be measured.
In the case of installing or taking out the object to be measured, the arm is retreated in a position distant from the object to be measured by the attitude change mechanism.
In the conventional contour measuring apparatus described above, when a power source is turned off after measurement work, each of the parts including the arm stops in a state just before the power source is turned off.
The arm may take an attitude distant from the object to be measured (or its installation part) in order to handle the object to be measured as described above, and in the case of stopping in this state, a distance between the arm and the installation part of the object to he measured remains increased.
When the arm stops with the distance increased, there are problems that, for example, a foreign substance gets into this distance (gap between the stylus and the arm, and the object to be measured or its installation part) or a worker touches accidentally and the stylus may break or chip due to an external force.
In the case of damaging the arm, for example, slightly bending the arm even when the stylus does not chip, high-accuracy measurement of the object to be measured cannot be made, with the result that replacement work of the arm is required and operational costs also increase.
As measures against such a stop state, attention is called to a worker manipulating the contour measuring apparatus so as to perform a manipulation of moving the stylus and the arm nearer to the installation part of the object to be measured in the case of turning off a power source after the completion of work.
However, since the attention only depends on artificial work, the manipulation may not be performed due to manipulation loss of the worker even when the attention is called, and a solution is not reached.
Incidentally, a detector for detecting swing displacement of the arm of the contour measuring apparatus includes an absolute type detector and an incremental type detector. The incremental type detector is well used since the incremental type detector is more inexpensive than the absolute type detector.
However, the incremental type detector has problems of being difficult to reduce processing and shorten time since origin return operation is indispensable every time the power source is turned on.